Bladder Stones (Cystic Calculi)

Calculi, popularly called stones can develop in many cavities in the body, e.g. the gall bladder, kidney, etc. They are commonly found in the urinary tract where they are termed uroliths. More specifically uroliths in the kidney are renal uroliths or renal calculi. The most common uroliths, bladder stones, are cystic uroliths or cystic calculi.

What common problems are associated with bladder stones?

• Blood stained urine (haematuria)
• Straining to urinate (dysuria)

These problems are not unique with bladder stones. They are the common symptoms of cystitis. Please see separate handout.

Haematuria occurs due to the irritation caused by the stones on the delicate lining of the bladder. This causes inflammation and then bleeding from the surface.  Bacterial infection also exacerbates the problem.

Dysuria can occur due to inflammation and irritation of the bladder wall, creating an urge to pass urine. Dysuria can also result from blockage by the stones.

When urine flows from the bladder is obstructed the bladder continues to fill with urine and this is an acutely painful condition. Often just touching the dog on the abdomen will cause cries of pain. Urethral blockage is particularly serious in male dogs since the long narrow urethra passes through the penis and blocks easily. Bitches with a much shorter urethra can frequently pass the stones which are causing the blockage after a period of discomfort and sometimes dysuria.

Why do they occur?

The precipitation-crystallisation theory is the most commonly accepted theory for bladder stone formation.

"The precipitation-crystallisation theory is the most commonly accepted theory for bladder stone formation."

One or more of the stone forming compounds is present in the urine in excessive amounts. This may be due to abnormalities in diet, or most commonly, bladder infection with certain bacteria. In certain cases the excess minerals may be due to a fault in body chemistry, which can occur in certain breeds.

Once the urine can dissolve no more of the compound, it is said to be supersaturated and the compound precipitates and forms minute crystals. These then clumpand stick together due to the mucus-like material that is found within the bladder. As these crystals grow other minerals in the urine become involved and so the stones enlarge.

Does this process happen rapidly?

This depends on various factors:

• Degree of bacterial cystitis (bladder infection)
• Quantity of crystal material available in the urine
• Degree of acidity of alkalinity (pH) of the urine. These are important factors controlling growth of the calculi. As a guide large single stones may take months or years to grow, often without causing any problems, whereas there are documented accounts of some stones that can develop in as little as two weeks resulting in a blockage.

How are cystic calculi diagnosed?

The signs of haematuria and dysuria discussed above are basically the signs of cystitis. A definite diagnosis of bladder stones depends on other signs and tests which include:

• Urine analysis and examination of a sample for stones or crystals
• Larger stones can sometimes be palpated (felt) through the abdominal wall.
• Most, but not all, bladder stones can be visualised with radiography.
• If radiography is inconclusive contrast radiography can be used. With this contrast material, (which is sometimes just plain air), is placed in the bladder and used to outline the stones if they are not radio opaque.
• Ultrasound scans.

What is the treatment?

If the stones cause obstruction this is an emergency. Treatment usually involves surgery. 

Until relatively recently surgery was the treatment of choice for all cystic calculi since it quickly alleviates pain and dysuria. The problem of recurrence however still has to be tackled. Commercial diets are now available on prescription which are designed to dissolve stones and prevent recurrence. The dietary approach has to be combined with antibiotics, and if necessary, drugs to change the acidity of the urine. This approach is not always successful since:

• Some stones are not capable of being reduced in size by the treatment strategy.
• It is slow to bring about improvement during which time the dog may still experience discomfort due to haematuria and dysuria.
• Some dogs refuse to accept the diet, which if mixed with other food is unlikely to be effective.

Is long term prevention feasible?

Following surgery, analysis of the stones allows future treatment to be planned effectively. Chronic cystitis has to be controlled which may involve periodic antibiotic treatment. Regular urine analyses and urine cultures to determine the bacteria present often has to continue long term. In the majority of cases the prognosis is good.